If the fraction of renewable energy in the German power market develops further in accordance with the concepts of the legislator, volatile, fluctuating sources of energy generation such as, for example, wind power or photovoltaics, from the year 2030 will provide more than 60% of the power requirement in Germany. If these sources in times of copious wind and sun with simultaneously low demand on the sides of the consumer are not to be down-regulated or even at times taken out of operation, then a store for receiving the surplus electrical energy will be required. A technically achievable and economically feasible possibility is offered for this purpose by the electrolytic generation of hydrogen from renewable electrical energy and the subsequent introduction thereof into the already existing gas grid or gas stores, which is also known as the concept “power to gas”.
Currently, a content of 5% of H2 in the gas grid is permitted, and an increase to a content of 10% is under discussion against the background of the required storage function. However, mixtures of H2 and natural gas, owing to the lower volumetric energy density of H2 (Hu=3 kWh/m3 S.T.P.) in comparison with that of natural gas (Hu˜10 kWh/m3 S.T.P.), have a lower heating value than pure natural gas.
The heating value/calorific value of natural gas mixtures (CH4, C2H6, C3H8 etc. and H2) is currently determined in what are termed delivery stations of the gas grid using cost-intensive multichannel gas chromatography measuring chambers, the cost of which exceeds 100,000 C. If, now, downstream of a delivery station, H2 is fed into the local distribution grid by a local energy producer, then at the consumers, in each case local calorific value sensors must be used in order to be able to determine the variable current calorific value of the H2/natural gas mixture with sufficient accuracy. In addition, the operating parameters of a gas heater depend on the chemical composition of the fuel gas provided, for which reason the engine control of the gas engines of combined heat and power plants, for an energetically optimal combustion, requires knowledge of the current composition of the fuel gas provided (in this case, in particular, the content of hydrogen in the H2/natural gas mixture). However, the multichannel gas chromatograph is too expensive for both tasks.